1. Field of the Invention
This invention relates to a noise insulating structure for improving silence characteristics within a passenger compartment of an automotive vehicle.
2. Description of the Prior Art
In a modern automotive vehicle, a plurality of interior parts are installed in a passenger compartment to maintain comfortableness for vehicle passengers. Of these interior parts, particularly a dash insulator, a floor carpet and a head lining are in close relation to silence characteristics within the passenger compartment, forming part of an interior structure of the passenger compartment. A typical conventional interior structure will be illustrated in FIGS. 3A to 3C. As shown in FIG. 3A, a conventional dash insulator 51 is constructed by successively laminating a low density layer 52 and a high density layer 53 on a dash panel p1 which serves as a partition wall disposed between an engine compartment and the passenger compartment. The low density layer 52 is usually formed of felt, polyurethane foam or nonwoven fabric. The high density layer 53 is usually formed of polyvinyl chloride sheet or rubber sheet in which filler is mixed. As shown in FIG. 3B, a conventional floor carpet 61 is constructed by successively laminating a low density layer 62, a high density layer 63 and a carpet skin layer 64 on a floor panel p2. The low density layer 62 is usually formed of a porous material such as felt, polyurethane foam or nonwoven fabric. The high density layer 63 is formed of a material which has no air-permeability, such as EVA sheet or polyethylene sheet in which filler is mixed. Additionally, as shown in FIG. 3C, a conventional head lining 71 is constructed by bonding a skin layer 73 on a base material 72 covering a roof panel p3. The base material 72 is usually formed of corrugated cardboard or plastic. A felt 74 is disposed between the base material 72 and the roof panel p3.
With the above conventional interior structure, the dash insulator 51 may somewhat reduce noise entering the passenger compartment from the engine compartment. The floor carpet 61 may somewhat reduce noise entering the passenger compartment from the engine compartment and the outside of the vehicle. The head lining may somewhat reduce noise entering the passenger compartment from the outside of the vehicle.
A noise insulating technique using above conventional interior structure is disclosed in "Automotive Vehicle Engineering Handbook", Design section, Pages 316-323, compiled by a corporation of Automotive Vehicle Engineering Society and published (the First Edition, on Mar. 1, 1991.